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Properties of Extrasolar Planets ASTR 241 Artist Impression: NASA Properties of Solar System Planets Terrestrial Planets Jovian Planets General Properties small size and mass high density rock & metal solid surface few moons, no rings close to sun, warm large size and mass low density H, He, H20, CH4, NH3, … no solid surface many moons, no rings far from sun, warm nearly circular orbits nearly all angular momenta vectors aligned “debris” - astroids, Kuiper belt, Oort Cloud Confirmed Planets - 2013 Transits RV Microlensing Imaging Solar System Pulsar Timing Data: exoplanets.org Exoplanet Detection Methods (planet = extrasolar planet = exoplanet) Doppler Method Transit Method How Do We Detect Exoplanets? Method #1: Doppler Method vradial = c Movie credit: ESO Mauna Kea Observatories Photo credit: Richard Wainscoat/Gemini Observatory/AURA/NSF Jupiter’s Doppler Signal Away from us Meters per second Orbit Period Toward us 13 meters per second! Planet Mass What We Found Meters per second 4.2 days! 0.45 Jupiter masses 51 Pegasi Hot Jupiter 1% of Sun-‐like stars have one Image: NASA Determination of Orbital Distance ! from Star to Planet Period = 4.2 days! ! Kepler’s 3rd Law: P2 = a3! ! Units: P in years, a in AU! ! Solve for a:! a = 0.05 AU! ! Proximity: Temp = 1800 C Determination of Planet’s Mass Conservation of Momentum: ! momentum of star = momentum of planet! ! MSTAR VSTAR = Mplanet Vplanet Solve for Mass of planet:! Mplanet = MSTAR VSTAR / Vplanet MSTAR : Star Masses are known ! (most are Sun-like) VSTAR from Doppler shift (semi-amplitude): ! 55 m/s What is Vplanet ? Vplanet = 2 π a / P! You know “a” from Kepler’s 3rd Law: P2 = a3 Can Determine Mplanet Mercury’s Orbit orbital distance = 0.39 AU! Temp = 800 degrees 51 Peg b’s Orbit orbital distance = 0.05 AU! Temp = 1,800 degrees Semi-major Axes (Orbital Distances) for Jovian Planets ~20% of Sun-like stars have a giant planet orbiting within 10 AU Orbital Eccentricities of Jovian Planets e = 0.01 e = 0.06 e = 0.05 e = 0.02 Orbital Eccentricity Fischer and Valenti (2004) Giant Planet-Metallicity Correlation Giant Planets are more common around stars rich in metals! This is a clue to planet formation! Systems of Planets Four-piter Two-piter Dinky Doppler Method of Planet Detection Measurable quantities planet mass ( M sin(i) ) orbital period (P) → semi-major axis (a) orbital eccentricity (e) orbital inclination (in some cases) planet multiplicity (# of planets per star) infer planet temperature host star properties (temperature, gravity, metal content) How Do We Detect Exoplanets? Method #2: Transit Method Question for Students: How big is the planet? π R2planet π 2 R star Transit Method of Planet Detection Measurable quantities planet size ( radius ) orbital period → semi-major axis orbital eccentricity (in exceptional cases) planet multiplicity dynamical interactions between planets infer planet temperature atmospheric properties Transit Example Kepler: A Mission to Find Earths Image: NASA Kepler-10 Light Curve 24 Kepler-10 Light Curve Period = 45.29 days 25 Kepler-10 Light Curve Period = 45.29 days 26 Period = 45.29 days Kepler-10 Light Curve Period = 45.29 days Kepler-10 Light Curve Period = 0.84 days Transit Depth: 0.00015 Kepler-10b Radius = 1.4 Rearth Period = 0.83 days Batalha et al. (2011) Kepler-‐10 Light Curve Planet Size and Mass Distributions Small planets are ubiquitous! Most stars have close-in “super-Earth” Planets! Why doesn’t the Solar System have a super-Earth? Known Planets - Masses and Radii Howard et al. 2013 (Nature) Possible Compositions for super-Earth Planets Different admixtures of H/He, water, rock, iron Weiss & Planet Density Distribution Planets Larger than ~1.5X Earth-size are low density. Smaller planets are high density. Kepler-78b - A Planet the Size and Mass of Earth Howard et al. 2013 (Nature) Multiple Planets Orbiting the Same Star are Common Our Solar System Video: Dan Fabrycky What about Earth-like Planets Image: NASA Kepler-186 Credit: NASA Image: NASA Erik Petigura Exoplanet Atmospheres Planets have slightly different sizes when measured at different wavelengths because of their atmospheres Properties of Solar System Planets Terrestrial Planets Jovian Planets General Properties small size and mass high density rock & metal solid surface few moons, no rings close to sun, warm large size and mass low density H, He, H20, CH4, NH3, … no solid surface many moons, no rings far from sun, warm nearly circular orbits nearly all angular momenta vectors aligned “debris” - astroids, Kuiper belt, Oort Cloud Properties of Extrasolar Planets Terrestrial Planets Intermediate Planets Jovian Planets they exist! small size and mass high density rock & metal (probably) solid surface (probably) moons?, rings? common < 1 AU, maybe > 1AU low eccentricities “super-Earths” or “sub-Neptunes” ubiquitous! common < 1 AU, maybe > 1AU low eccentricity orbits “flat” planetary systems (not-tilted orbits) large size and mass low density H, He, H20, CH4, NH3, … no solid surface moons? rings? all orbital distances all eccentricities many in tilted orbits prefer metal-rich stars Measurable Properties of Extrasolar Planets Doppler Method Transit Method planet mass ( M sin(i) ) orbital period -> semi-major axis orbital eccentricity orbital inclination (in some cases) planet multiplicity infer planet temperature host star properties (Temp, grav., metal content) planet size ( radius ) orbital period -> semi-major axis orbital eccentricity (in exceptional cases) planet multiplicity dynamical interactions between planets infer planet temperature atmospheric properties Properties of Extrasolar Planets Terrestrial Planets Intermediate Planets Jovian Planets they exist! small size and mass high density rock & metal (probably) solid surface (probably) moons?, rings? common < 1 AU, maybe > 1AU low eccentricities “super-Earths” or “sub-Neptunes” ubiquitous! common < 1 AU, maybe > 1AU low eccentricity orbits “flat” planetary systems (not-tilted orbits) large size and mass low density H, He, H20, CH4, NH3, … no solid surface moons? rings? all orbital distances all eccentricities many in tilted orbits prefer metal-rich stars The End